26 ESSENTIALS OF BOTANY 



kept in too moist an atmosphere, or very few root-hairs 

 will be formed. Examine with the magnifying glass 

 those parts of the root which have these appendages. 



Try to find out whether all the portions of the root are 

 equally covered with hairs, and, if not, where they are 

 most abundant (see also Fig. 10). 



The root-hairs in plants growing under ordinary condi- 

 tions are surrounded by the moist soil and wrap them- 

 selves around microscopical particles of earth (Fig. 11). 

 Thus they are able to absorb rapidly through their thin 

 walls the soil-water with whatever mineral substances it 

 has dissolved in it. 



35. The Young Stem. — The hypocotyl, or portion of 

 the stem which lies below the cotyledons, is the -earliest 

 formed portion of the stem. Sometimes this lengthens but 

 little, as in Fig. 2 ; often, however, as the student knows 

 from his own observations, the hypocotyl lengthens enough 

 to raise the cotyledons well above ground, as in Fig. 9. 



The later portions of the stem are considered to be 

 divided into successive nodes (places at which a leaf, or 

 a scale which represents a leaf, appears) and internodes 

 (portions between the leaves). 



The student should watch the growth of a seedling bean 

 or pea and ascertain by actual measurements whether the 

 internodes lengthen after they have once been formed, and, 

 if so, for how long a time the increase continues. 



36. The First Leaves. — The cotyledons are, as already 

 explained, the first leaves which the seedling possesses, — 

 even if a plumule is found well developed in the seed, it 

 was formed after the cotyledons. In those plants which 

 have so much food stored in the cotyledons as to render 

 these unfit ever to become useful foliage leaves, there is 



